The percentage of staff suffering work-related stress fell from 39% in 2003 to 33%, while the staff witnessing errors with potential harm for patients fell from 49% to 38% over the same period.

Ms Walker said: "It is a credit to trusts that during a period of change staff say they are less stressed. And the progress we have seen in safety is to be commended."

But she added trusts needed to "redouble their efforts" to protect staff - 31% of workers experienced violence or abuse from patients, a figure which has remained stable over recent years.

NHS Employers' Deputy Director Alastair Henderson said: "In comparison with many organisations, satisfaction with the NHS as an employer is still good, but we need to work hard to make sure the NHS remains a place people want to work.

"There is clearly work that still needs to be done particularly on tackling bullying and harassment."

And Unison health spokeswoman Karen Jennings added: "This survey confirms that a much more robust deterrent is needed to crack down completely on abuse and attacks on health staff."

The poll, carried out in 2006, will be fed into the Healthcare Commission's annual assessment of NHS trusts.